1. Field of the Invention
The disclosure generally relates to the subsea riser supports. Specifically, the disclosure relates to the subsea riser supports for laterally disposed risers that are stressed by gravity forces.
2. Description of the Related Art
Not all subsea risers are disposed vertically. Risers can lay laterally from an oil or gas well across a seabed before curving upward to an offshore platform at the water surface. This configuration is especially true, when a field is developed for production with multiple risers spaced around the field that converge upward to an offshore platform.
Further, not all seabeds are smooth, level surfaces, despite the many illustrations in literature. Rocky abutments, canyons, cliffs, and other escarpments must be crossed by the risers to connect with the offshore platform. Gravity forces on the risers tend to bend the risers, as they lay in a lateral orientation across the subsea structures and cause undesirable stress, as illustrated in FIG. 1. A seabed 2 can have many projections and depressions in its surface. A riser 4 will conform to some degree to the surface due to the gravity forces, causing bending stresses on the riser. While risers can be designed to withstand the stress, the design can be costly in material and expense
Prior efforts generally involve buoys to support the riser across the unlevel surface in a neutral buoyancy mode. Some examples are illustrated in FIGS. 2 and 3. In FIG. 2, a floating arch is preinstalled by securing a tether 8 with an anchor 6 to the seabed and coupling the tether 8 to a floating buoy 10. The riser 4 is supported by the floating buoy tethered to the seabed to form the supporting arch. In FIG. 3, floating buoys 12 are installed to the riser 4 and float the riser over the different structural changes in the seabed. A variation is shown in FIG. 3 in that a floating buoy 16 can be connected with a tether 14 to the riser 4 to accomplish the same purpose.
Because such typical designs depend on floatation, the degradation of the buoys over life of service can cause buoy failure and with the failure potential riser failure. Additionally, the costs and effort in establishing a buoy-based system can be substantial.
There remains then a need to provide a long-lasting alternative to support a riser across elevational changes in a seabed.